4.5.6.7.8.9.Raise the mask to your outthrust chin andbring the head harness over the back ofyour head.Center the head harness pad on the backof your head and adjust the bottom strapsas necessary for proper fit.Close the outlet valve with the heel of thehand and exhale forcibly to clear the maskof contaminated air.Test the mask for possible leakage byplacing your palms over the canisters andinhaling normally until the mask collapsesagainst your face and remains collapsed forapproximately 10 seconds.Resume normal breathing.Replace headgear and close the carrier flap.The protective mask outlet valve sometimessticks closed because saliva or sweat has dried onit. If this occurs, you may loosen the valve byblowing into the valve or by massaging the valve.The valve may be massaged with the valve coverpartially removed as shown in figure 6-4.CANISTER REPLACEMENT. A pair ofreplacement canisters for the ND Mk V mask isprovided in a hermetically sealed coffee cancontainer. While sealed in this container, thecanisters have an indefinite shelf life. Therefore,the container seal should not be broken until thecanisters are to be mounted on the mask. Onceunsealed, the container should not be resealed,and the canisters should be permanently removedfrom it.The following procedures are used forremoving and replacing canisters on the NDMk V mask. To remove each canister fromthe facepiece, you should take the followingactions:1. Roll approximately one-third of the rubberapron back over the edge of the canister.2. Slide the canister off the holder.To install new canisters on the facepiece, youshould proceed as follows:1.2.3.4.Remove the canisters from the hermeticallysealed container.Roll the rubber apron of each canistercompletely over the outer edge of thecanister.Position each canister snugly against itsholder so that the holder contacts theperforated plate of the canister at all pointsof its outer edge.Roll the rubber apron of each canister overthe back of the canister holder.CARE OF THE ND MK V MASK. Becauseof the importance of the mask, it should bemaintained in an efficient operating condition.Careful attention should be given to stowing,cleaning, handling, and inspecting the mask toprolong its useful life.The mask should be stowed in a cool, dry,dark area free from solvents and their vapors. OilFigure 6-4.-Correcting sticking outletpartially removed.valve with coverand gasoline vapors weaken the rubber and areespecially damaging to the activated charcoalin unsealed canisters. The mask must be keptdry. Moisture causes rotting of parts, corrodingmetal, deteriorating canisters, and mildewingcarriers.The mask should be thoroughly cleaned withsoap and water and dried before it is stowed. Ifthe mask was previously used and is to be issuedto another person, it should be sterilized with a6-12